This invention relates particularly to a system for detecting an underinflated tire of a vehicle; and more generally to a system for detecting a difference in the rolling speed of one vehicle wheel relative to another, which may be an indication of underinflation.
Underinflated tires on any vehicle are a potential hazard, particularly so with respect to an aircraft wherein the loss of full support of one wheel of a landing gear may result in serious damage and, possibly, loss of control of the aircraft.
The undercarriages of modern high capacity aircraft must be capable of withstanding enormous loadings and shocks, and very high landing and takeoff speeds without significant hazards to the craft occupants and cargo. Such undercarriages may fail to perform as intended, if any one of the tires happens to be flat or even underinflated. The serious nature of such problems can be readily appreciated when it is realized that one flat or inadequately inflated tire of a multiple set may not be easily discerned on casual visual inspection and yet may be grossly damaged, may cause other tires of the set to be overloaded and damaged, or may overheat to the point of inflammability as a consequence of high speed runway travel of the craft.
Separate tire pressure readings cannot be taken easily and economically from outside by a ground maintenance crew each time a many-wheeled aircraft prepares for takeoff. Equipment which routinely comes to mind for automatic sensing of rotatable-wheel tire pressures may be expected to involve elaborate and undesirably weighty provisions for telemetering.
It is desirable, however, to provide a system, particularly for use with aircraft, which will advise the operators of the aircraft of an underinflated tire while the aircraft is rolling on the ground. In addition to the safety factor provided by such a system, the system enables repair or replacement of the offending tire with a minimum of delay and resultant saving of costly aircraft time.
The detection of an underinflated tire is based on the detection of an increase in speed of the wheel carrying that underinflated tire, considering that when the tire is underinflated it will have a smaller rolling radius and will therefore rotate faster than a wheel with a normally inflated tire. In the following specification the term "rolling radius" means the distance between the wheel support surface and the wheel axis of rotation. The term "rolling circumference" is the effective tire circumference related to the rolling radius. The detection system must be quite sensitive considering that most modern high capacity aircraft are equipped with landing gear structures which involve a multiplicity of inflated tires arranged in sets or "bogies" associated with different ones of several main struts, and these sets include side-by-side pairs of tires. The difference in rolling radius of the underinflated tire then will be affected by the fact that a substantial portion of the load is carried by the adjacent tire.
An object of this invention is to provide a system for detecting a difference in the speed of rotation of one wheel relative to another, in a rolling vehicle such as an aircraft.
Another object of this invention is to provide a system for detecting an underinflated tire in a rolling vehicle, such as an aircraft.
A further object of this invention is to provide a system for detecting an underinflated tire in a rolling vehicle, by comparing the speed of rotation of two different vehicle wheels.
Still another object of this invention is to provide a system for detecting an underinflated tire in a rolling vehicle, which system is economic to manufacture, reliable in operation, and responsive to very small changes in tire inflation pressure.
Another object of this invention is to provide a system for detecting a dragging brake in a rolling vehicle.
A still further object of this invention is to provide a system for detecting a change in rotational speed of one wheel relative to another, in a rolling vehicle such as an aircraft, which system is responsive to a very small increase in the speed of one wheel relative to the other resulting from loss of pressure in the one wheel tire.
These objects are attained in an advisory system for detecting and indicating a difference in speed of a pair of load bearing wheels of a vehicle. Broadly the system includes first and second signal generating means associated, respectively, with first and second wheels. Each signal generating means includes wheel speed transducer means coupled to a wheel for producing a DC voltage wheel speed signal which is proportional in linear relation to the rotational speed of the wheel. An electric comparator means produces an output signal responsive to differences between two input signals applied thereto; and an electrically operated fault signaling means is responsive to an output signal from the comparator means. The system includes means applying as input signals to said comparator means, a first wheel speed signal related to the first signal generating means, and a second wheel speed signal related to the second signal generating means. The comparator means produces an output signal to activate the fault signaling means when one of said wheel speed signals changes in relation to the other, with the other wheel speed signal functioning as a reference signal.
More particularly the electric comparator means includes first and second separate comparator means; and the fault signaling means is responsive to an output signal from either of said comparator means. The input signals applied to the first comparator are the first and second wheel speed signals, with the second wheel speed signal functioning as the reference signal; generating means; the first comparator means producing an output signal to activate the fault signaling means when the first wheel speed signal changes in relation to the reference signal. The input signals applied to the second comparator means are the first and second wheel speed signals with the first wheel speed signal functioning as the reference signal; and the second comparator means produces an output signal to activate the fault signaling means when the second wheel speed signal changes in relation to the reference signal.
The novel features and the advantages of the invention, as well as additional objects thereof, will be understood more fully from the following description when read in connection with the accompanying drawing.